1. Field of the Invention
The present invention relates to a location registration method and a paging method in a mobile communication system, a mobile communication system, a base station, a communication control method, a mobile station, and a communication control program; and, in particular, to a location registration method and a paging method for a mobile station which is in a sleep mode in a wireless packet communication, the mobile station, a base station, a mobile communication system constituted by including them, a communication control method, and a communication control program.
2. Related Background Art
A digital car phone system referred to as PDC (Personal Digital Cellular) has been known (ARIB RCR STD-27H: digital car phone system standard). This system employs a multilayer location registration area scheme in which, while a location registration area where each mobile station registers a location information is divided into a plurality of groups, each group has a plurality of layers. The location registration area differs from one group to another, which is effective in preventing location registration traffic from being centered at specific cells in area boundaries. Each mobile station is notified of location registration area information of the group to which it belongs by notification information from a base station, compares thus notified location registration area information with its own registered location registration area information, and registers its location information if the information differs from the registered information. A characteristic feature here is that the location registration areas corresponding to the groups to which each mobile station belong have substantially the same size among all the mobile stations regardless of the traffic specific to the mobile stations. Since the location registration areas are multiplexed, so that a location registration area centered at a cell in which a mobile station always exists is selectively registered, the probability of traversing location registration areas is reduced, whereas a hysteresis is provided, which is effective in restraining location registration signals from frequently being transmitted, i.e., suppressing fluttering.
Japanese Patent Application Laid-Open No. HEI 5-3581 discloses a location registration and paging scheme for a mobile communication system. This scheme is concerned with a mobile communication system in which base stations determine overlapping location registration areas in an autonomous decentralized manner, whereas each mobile station receives location registration area information broadcasted from a base station, compares its registered location registration area information with the location registration area information obtained from the broadcasted information, and registers a location information when it moves to a cell not included in the location registration area information own registered thereby. Each mobile station stores cells passed thereby after the location registration as route information and notifies a base station of the route information at the time of the next location registration. Here, the base station absorbs cells having a large amount of route information into a location registration area, thereby reconstructing the location registration area.
This scheme is targeted at connection-oriented mobile communication systems, in which a line-switching station broadcasts a call signal for a mobile station to all the base stations belonging to a location registration area. The number of cells included in the location registration area is increased/decreased according to the amount of traffic. Namely, the number of cells included in the location registration area is decreased when the paging traffic to a mobile station exceeds a predetermined amount, whereas the number is increased when the paging traffic received from the mobile station exceeds a predetermined amount, whereby the paging traffic and location registration traffic can be kept in balance.
The conventional techniques such as those mentioned above are employed in connection-oriented mobile communication systems, and fail to address problems specific to packets in wireless packet communication systems. Namely, they fail to take account of how to conserve battery of mobile stations which are in idle state when a connection cannot clearly be associated with a physical link, thus being unsuitable for wireless packet communications. Effective battery conservation method in packet communications is one in which a mobile terminal registers its location to which belongs as in line-switching to receive paging signals periodically. However, this method may be problematic in that the location registration occurs frequently when the location registration area is small, thereby increasing the traffic for location registration.
Though the location registration traffic can decrease if the location registration area is made larger, this may be problematic in that the traffic of paging upon incoming calls increases. Therefore, it is necessary that the size of a location registration area taking account of the traffic balance between location registration traffic and paging traffic upon incoming calls be set dynamically. Battery conservation effect depends on location registration frequency and paging interval. Consequently, they are required to be controlled flexibly according to traffic characteristics of individual terminals in connectionless packet communications.
Though multilayer location registration areas are set in the above-mentioned digital car phone system in order to prevent location registration traffic from increasing in specific cells, there is a fear of failing to keep a traffic balance when applied to packet communications, since the respective location registration areas corresponding to the individual groups have the same size.
The location registration and paging system for a mobile communication system disclosed in the above-mentioned Japanese Patent Application Laid-Open No. HEI 5-3581 sets a location registration area while taking account of only the size of location registration area according to the amounts of location registration traffic and paging traffic without control considered the traffic characteristics of each mobile station specific to packet communications, whereby the location registration area does not always attain an optimal size.